Two-stage carburetion



Oct. 10, 1961 H. A. CARLSON 3,003,483

TWO-STAGE CARBURETION Filed Nov. 28, 1958 5 Sheets-Sheet 1 INVENTOR.

HAROLD A CARLSON ATTORNEY Oct. 10, 1961 H. A. CARLSON TWO-STAGE ,CARBURETION 5 Sheets-Sheet 2 Filed NOV- 28, 1958 INVENTOR. HAROLD A. CARL SON ATTORNEY Oct. 10, 1961 H. A. CARLSON 3,

TWO-STAGE CARBURETION Filed Nov. 28. 1958 5 Sheets-Sheet 4 FIG 7.

INVENTOR. HAROLD A.CARLSON ATTORNEY Oct. 10, 1961 H. A. CARLSON TWO-STAGE CARBURETION 5 Sheets-Sheet 5 Filed Nov. 28, 1958 FIGQ.

FIG .I I.

ATTORNEY 3,003,488 TWO-STAGE CARBURETION Harold A. Carlson, Brentwood, Mo., assignor to ACF Industries, Incorporated, New York, N.Y., a corporation of New Jersey Filed Nov. 28, 1958, Ser. No. 776,975 19 Claims. (Cl. 123-127) This invention relates to carburetion systems, and more particularly to multi-stage carburetion systems for internal combustion engines.

One type of multi-stage carburetion system used on automotive engines (particularly on V-8 engines) comprises three dual carburetors for supplying a mixture of fuel and air to the intake manifold of the engine, one of the dual carburetors being a primary carburetor for supplying fuel mixture in the lower power range and each of the other two being a secondary carburetor for supplementing the supply of. fuel mixture in the upper power range. It will be understood that a dual carburetor is a carburetor having two mixture conduits through which air may flow to the intake manifold under control of a dual throttle comprising two throttle valves, one in each conduit, on a throttle shaft common to both valves, and having means for supplying fuel to the conduits for admixture with air flowing therethrough. This type of system or installation is referred to as a triple dual system or installation, and requires the use of a special intake manifold having a generally central pair of primary openings, and two additional pairs of secondary openings located between the central pair and the front and rear ends of the manifold. The primary carburetor is mounted generally centrally of the intake manifold with its two mixture conduits registering with the central pair of primary openings. The secondary carburetors are mounted on the intake manifold between the primary carburetor and the front and rear ends of the manifold with their mixture conduits registering with the respective pairs of secondary openings.

The dual throttle of the primary carburetor is controlled in the usual manner by the accelerator pedal of the automotive vehicle, the usual return spring being provided biasing the throttle valves thereof toward closed position. Means is provided for opening the dual throttles of the secondary carburetors in response to opening of the throttle of the primary carburetor in such manner that the former are not opened until the latter is part-way open. Thus, while the primary carburetor supplies fuel mixture throughout the entire operating range of the engine, the secondary carburetors come into operation only in the upper power range. Heretofore it has United States aten-t been the practice, in order to maintain the throttles of the secondary carburetors tightly closed in the lower power range, to provide each of the secondary carburetors with a relatively strong torsion spring biasing its throttle toward closed position. When such springs are used, and their return bias is added to the return bias of the return spring operative on the throttle of the primary carburetor, there is an annoying resistance to operation of the accelerator pedal in the upper power range, since there is a triple spring resistance to pedal operation.

Accordingly, it is an object of this invention to provide a multi-stage system of the class described in which means is provided for applying suflicient force to the throttles of the secondary carburetors to maintain them closed in the lower power range before the throttle of the primary carburetor has opened to the point Where the throttles of the secondary carburetors start to open, without imposing objectionable resistance to pedal operation in the upper power'range after the throttles of the secondary carburetprshave started to open.

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Patented Oct. l0, 961

Morespecifically, it is an object of the invention to provide means for applying sufficient force to the throttles of the secondary carburetorsto maintain them closed in the lower power range, and for reducing this force inthe upper power range so that pedal operation is eased since the driver of the vehicle then does not have to overcomeany substantial closing force on the throttle valve means of the secondary carburetors.

In general, the objects of the invention are attained by providing a vacuum-operated means for holding the throttle of each secondary carburetor closed with a force depending on the vacuum therein, this vacuum-operated means being responsive to opening of the throttle of the primary carburetor to reduce the vacuum thereby to reduce the force. With this arrangement, the vacuum-' operated means is effective to hold the throttle of each secondary carburetor'closed in the lower power range, becoming relatively ineffective in theupper power range so as not to impose objectionable resistance to pedaloperation.

In one embodiment of the invention, reduction of vacuum in the vacuum-operated means is effected by connecting it to the intake manifold. Sinces the vacuum in the intake manifold inherently decreases on opening the throttle of the primary carburetor, the vacuum in the vacuum-operated means decreases on opening the throttle of the primary carburetor. Y

In another embodiment of the invention, reduction of vacuum in the vacuum-operated means is effected by con necting it to a source of vacuum such as the usual vacuum booster pump on the engine, with a control valve in the connection responsive to opening of the throttle of the primary carburetor to reduce the vacuum in the vacuum: controlled means, as by venting the latter when the throttle of the primary carburetor is opened a predeter: mined amount. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being in dicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a view in elevation illustrating the primary and the two secondary carburetors mounted on the engine of an automotive vehicle;

FIG. 2 is a perspective view of the engine as viewed from one side (the right side) thereof, showing the three carburetors;

FIG. 3 is a perspective view of the engine as viewed from the other side (the left side) thereof, also showing the three carburetors; f

FIG. 4 is a side elevation of the three carburetors, as, viewed from the same side as FIG. 3, on a larger scalev than of FIG. 3, and With'parts broken away and shown in section;

FIG. 5 is an enlarged plan view of the primary carbu-. retor (the central carburetor); F1216; 6 is a vertical section taken on line 6-6 ofv FIG. 7 is a view in elevation of one side of the carburetor shown in FIG. 5 (that side which is at the bottom of FIG. 5 and which is the left-hand side of the carbu retor as it is mounted on the engine);

FIG. 8 is a view in elevation of the other side of the carburetor (its right-hand side);

FIG. 9 is a vertical section taken on line 9-9 of FIG. 5;' v v FIG, 10 is a fragmentary detail section of oneof the: secondary carburetors; I 1.

FIG. 11 is a plan view illustrating. the intake manifoldflun...

FIG. 12 is a side elevation of the primary carburetor illustrating a modification in which a control valve is provided; and,

FIG. 13 is a section illustrating the operation of the control valve shown in FIG. 12.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Referring to the drawings, there is indicated at A in FIG. 1 an automotive vehicle having an engine E on which there are three carburetors '1, 2 and 3. Fuel is supplied to these carburetors from the fuel tank 7 of the vehicle. As shown, there may be an electric pump 9 in the fuel tank for pumping fuel from the tank 7 through a line 11 to a mechanical fuel pump 13 (see FIG. 2) on the engine. Pump 13 is operated by the engine and is adapted to pump fuel to the three carburetors through a line 15. Each of the carburetors 1, 2 and 3 is shown as being of the type having two mixture conduits, referred to as a dual carburetor. With three of these carburetors on the engine, the carburetion system is referred to as a triple dual system. The three carburetors are mounted in line on the intake manifold 17 of the engine, with carburetor 1 located approximately centrally of the length of the manifold, carburetor 2 toward the forward end of the manifold, and carburetor 3 toward the rearward end of the manifold. Carburetor 1 is a so-called primary carburetor, being adapted to supply a mixture of fuel and air to the intake manifold throughout the entire operating range of the engine. Carburetors 2 and 3 are so-called secondary carburetors, being adapted to supply a mixture of fuel and air (supplementing that supplied by primary carburetor 1) only in the upper power range of the engine. On each carburetor is an air filter 19.

As shown best in FIGS. 4-9, primary carburetor 1 comprises a main body section 21 to the top of which is secured an air horn section 23 and to the bottom of which is secured a throttle body section 25. The main body section and throttle body section are formed to provide two vertical mixture conduits, each designated 27, located side-by-side. These may be referred to as primary mixture conduits. The main body section 21 is formed so that each mixture conduit 27 has a restriction 29 toward the lower end of that part of the conduit in the main body section forming a main venturi. The throttle body section 25 is formed so that the portions of the mixture conduits 27 therein are cylindrical, constituting throttle bores 31. A throttle shaft 33 extends from side-to-side of the throttle body section across these bores and carries two throttle valves 35, one for each bore. Each of these may be referred to as a primary throttle valve. Fixed on shaft 33 at one end thereof is a throttle arm 37. To this arm 37 of the primary carburetor 1 is connected the usual accelerator pedal operated rod 39 (see FIG. 4), arrangement being such that when the pedal is depressed, arm 35 and shaft 33 are rotated clockwise as viewed in FIGS. 4, 6 and 9 to open the throttle valves, and when the pedal is released, the throttle valves are returned in closing direction under the bias of the usual return spring 40.

The main body section 21 of the primary carburetor 1 is formed to provide a fuel bowl 41 forward of the two mixture conduits 27. The bowl has an inlet 43 through which it is supplied with fuel from pump 13 under control of a needle valve 45 which is in turn controlled by a float 47. Float 47 controls valve 45 to block the inlet when the fuel in the bowl reaches a predetermined level. A bowl vent is indicated at 49. In each mixture conduit 27 is a nozzle body 51 including a small venturi 53 (sometimes referred to as the;primary venturi). Each nozzle body is mounted on a portion of the main body section having a vertical well 55 therein (see FIG. 9). This well receives fuel from the bowl via a passage 57 under control of the usual vacuum-operated metering-rod 59 which meters the flow from the bowl to the .well through a metering jet 61. Rod 59 is controlled by intake manifold vacuum, being raised when manifold vacuum decreases to increase the flow and vice versa. A perforated tube 63 extends down from the nozzle body into the fuel in the well and supplies the fuel to a main nozzle 65 opening into the venturi 53 for high speed engine operation. An idle tube 67 also extends down into the well for supplying fuel for idling to idle passage 69 having the usual economizer restriction 71 thereon. The usual idle bleed is indicated at 73. At 75 in FIG. 6 is indicated the usual accelerator pump operated by a linkage such as indicated at 77 from the throttle arm 37 for positively pumping fuel from the bowl to a pump jet cluster 79 which delivers the fuel into the mixture conduits 27 when the throttle valves 35 are opened.

The primary carburetor 1 includes a choke comprising a choke valve shaft 81 extending across the air horn section 23 from side-to-side of the carburetor and carrying the usual choke valve 83. As shown, the choke is of the so-called cross-over type used on V-8 engines under control of a thermostatic coil located in a heat pocket in the so-called cross-over passage of the exhaust manifold of the engine. The choke valve is connected by a link 85 to a piston 87 slidable in a cylinder 89 formed laterally on the air horn section. Cylinder 89 has a longitudinal slot 93, and this slot is adapted for communication with the intake manifold via a vacuum passage so that the piston is responsive to manifold vacuum. At 97 in FIG. 7 is indicated the usual fast idle cam, the position of which is controlled by a link 99 connected to the choke shaft 81. This cam is engageable by the usual screw 101 on the throttle arm 37.

As shown herein, engine E is a V-8 engine, and intake manifold 17 is a special triple-dual manifold to accommodate the triple-dual carburetion system. As appears in FIG. 11, the four cylinders in the left bank of engine cylinders are numbered C1, C3, C5 and C7 in order from front to rear of the engine, and the four cylinders in the right bank are numbered C2, C4, C6 and C8. Manifold 17 has a so-called high runner 103 indicated in dash lines in FIG. 11 extending lengthwise thereof with lateral branches 105, 107, 109 and 111 therefrom to the intake valves indicated at V for cylinder C1, C4, C6 and C7. Manifold 1.7 also has a socalled low runner 1 13 (at a lower elevation than runner 103 and laterally offset from runner 103) indicated in dotted lines in FIG. 11 with lateral branches 115, 117, 119 and 121 therefrom to intake valves V for cylinders C2, C3, C5 and C8. Manifold 17 has a forward pair of top openings 123 leading down into the runners 103 and 113 at their forward ends, an intermediate pair of top openings 125 leading down into the runners 103 and 113 generally centrally of their length, and a rearward pair of top openings 127 leading down into the runners 103 and 113 at their rearward ends. Primary carburetor 1 is mounted on top of the intake manifold with its mixture conduits registering with openings 125. As shown herein, the secondary carburetors 2 and 3 are dual carburetors basically the same as the primary carburetor 1 except that such elements as the choke valve, the accelerator pump and the fast idle cam may be omitted. It will be understood that the secondary carburetors need not be identical to the primary carburetor. For example, they may have smaller mixture conduits. Secondary carburetor 2 is mounted on top of the intake manifold with its mixture conduits registering with openings 123 and secondary carburetor 3 is mounted on top of the intake manifold with its mixture conduits registering with openings 127.

Means is provided for opening the throttle valves of the secondary carburetors 2 and 3 (which are the same as valves 35 of primary carburetor 1) upon opening the throttle valves of the primary carburetor 1 beyond a predetermined position. As shown, this means comprises rods 129 and 131 pin-connected at 132 to the throttle arm of the primary carburetor 1 and extending to the throttle arms 37a of the secondary carburetors where they have lost-motion connections with the latter arms such that arm 37 of carburetor 1 swings through a predetermined arc before arms 37a of carburetors 2 and 3 start to swing. The lost-motion connections are shown as being provided by forming rod 129 with a slot 133 in its end where it is connected to the throttle arm of carburetor 2 and by forming rod 131 with a slot 135 in its end where it is connected to the throttle arm 37a of carburetor 3. Slot 133 in rod 129 receives a pin 137 on arm 37a of carburetor 2. Slot 135 in rod 131 receives a pin 139 on arm 37a of carburetor 3. When all three throttle arms are in closed position as shown in FIG. 4, rods 129 and 131 occupy retracted positions wherein the left ends of slots 133 and 135 are contiguous to the pins 137 and 139. When the throttle arm 37 of primary carburetor 1 is swung clockwise from its FIG. 4 position to open the throttle valves of primary carburetor 1, rods 129 and 131 are driven to the left. During the initial phase of this movement, no motion of arms 37a of carburetors 2 and 3 occurs. However, when the rods move far enough to the left for engagement of the right ends of slots 133 and 135 with pins 137 and 139 and continue on, thearms 37a of the secondary carburetors 2 and 3 are swung clockwise to open the throttle valves of carbu retors 2 and 3. The radius of pins 137 and 139 with respect to the axes of the throttle arms 37a of carburetors 2 and 3 is so related to the radius of the pin connection 132 with respect to the axis of throttle arm 37 of the primary carburetor 1 and the slots 133 and 135 are of such length, that the throttle valves of secondary carburetors 2 and 3 start to open when the throttle valves of primary carburetorl are approximately half open, for example, and reach fully open position when the throttle valves of primary carburetorl reach fully open position.

The throttle, valves of the primary carburetor 1 are always biased toward their closed position because of the bias of return spring 40 on arm 37, but spring 40 is ineffective to provide a closing bias on the throttle valves of the secondary carburetors .2 and 3 in the low speed range when the throttle valves of primary carburetor 1 are partly open. This is because rods 129 and 131 are then to the left of their FIG. 4 closed position, and pins 137 and 139 are free in slots 133 and 135 of the rods. In accordance with this invention, each of the secondary carburetors 2 and 3 is provided with a vacuum motor 141 for maintaining their throttle valves 35 tightly closed in the low speed range. Motor 141 comprises a cup 143 closed by a diaphragm 145 held .on the cup by a cover 147. The cup 143 and diaphragm 145 define. a vacuum chamber 149. In the base of the cup 143 is a nipple 151 providing for connection of a vacuum line 153 to the chamber 149. A rod 1555 extends from the diaphragm through an opening 157 in the cover. A link 158 connects this rod to the throttle arm 37a of the secondary carburetor. A relatively weak spring 161 may be interposed between the diaphragm and the base of the cup biasing the rod 155 outward. The motor 141 is mounted on the carburetor 2 or 3, as the case may be, by means of a bracket 163 in such position that with vacuum in chamber 149, rod 155 is drawn into the motor to pull the throttle arms 37a of the carburetor in closing direction via the link 159. The vacuum line 153 connected to the motor 141 on each secondary carburetor 2 and 3 is connected to a vacuum port 165 which opens into one of the mixture conduits of the respective carburetor below or posterior to the throttle valve therein (see FIG.

Operation is as follows:

When the engine E is in operation, and the throttle .valves of all three carburetors 1, 2 and 3 are substantially closed, the vacuum in the intake manifold 17 and in the mixture conduits 27 of secondary carburetors 2 and 3 below the throttle valves 35 therein is relatively high.

Since the vacuum chambers 149 of the-vacuum motors 141 on carburetors 2 and 3 are in communication via vacuum lines 153 with the mixture conduits 27 of carburetors 2 and 3 posterior to the throttle valves 35 therein, the diaphragms of the motors are pushed up by atmospheric pressure with relatively high force to hold the throttle valves 35 of carburetors 2 and 3 tightly closed. While the vacuum decreases when the throttle valves 35 of the primary carburetor 1 are opened, it is sufiicient to maintain the throttle valves 35 of secondary carburetors 2 and 3 tightly closed during the low speed range. .When the throttle valves of the primary carburetor 1 are opened to the point Where the throttle valves of the secondary carburetors 2 and 3 are about to be opened by rods 129 and 131, the vacuum will have decreased to such a low value that opening of the throttle valves of the secondary'carburetors 2 and 3 by rods 129 and 131 may then proceed with negligible resistance from the motors 141.

FIG. 12 illustrates a modification in which reduction of vacuum in the motors 141 is effected by connecting them to a source of vacuum, such as the usual vacuum booster pump which is conventionally provided (usually as an'adjunct of the mechanical fuel pump 13) with a control valve 171 in the connection responsive to opening of the throttle valves of the primary carburetor 1 to reduce the vacuum in motors 141. This control valve may be of a conventional type which is sometimes referred to as a vacuum switch. It is mounted on the primary carburetor 1 and actuated by the throttle arm 37 of the primary carburetor. By way of illustration, the control valve 171 comprises a cylinder 173- having a port 175 for connection as at 176 to lines 153 connecting to the motors 141, a port 177 forconnection to the source of vacuum such as the vacuum booster pump, and a vent port 179. Slidable in the cylinder 173 is a plunger 181 having a groove 183 adapted when the plunger is in the raised position illustrated in FIGS. 12 and 13 to connect ports 175 and 177 so as to supply vacuum to the motors. The plunger is movable downward from this raised position to a lowered position in which groove 183 connects ports 175 and 179 to vent the motors. The plunger is shown as being operated by means of a link 185 connecting the throttle arm 37 of the primary carburetor 1 to a rocker 187 pivoted at 189 on the carburetor "1, and having a connection at 191 with the plunger.

The arrangement is such that when the primary throttle arm 37 is in its retracted position with the throttle valves 35 of the primary carburetor 1 closed, the plunger 181 is raised so that vacuum is supplied to the motors 141 to hold the throttle valves 35 of the secondary carburetors 2 and 3 tightly closed. When the throttle valves of the primary carburetor 1 are opened to the point where the throttle valves of the secondary carburetors 2 and 3 are about to be opened by rods 129 and 131 (the same as in FIG. 4), groove 183 in the plunger 181 comes into position providing for communication between ports 175 and 179 to vent the motors 141. This removes the closing bias of motors 141 on the throttle valves of, the secondary carburetors 2 and 3.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could bemade in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A multi-stage fuel mixture supply system for an internal combustion engine comprising means providing a primary mixture conduit and a secondary mixture conduit adapted to supply a mixture of fuel and air to the engine, a primary throttle valve in the primary mixture conduit, a secondary throttle valve in the secondary mixture conduit, lost-motion linkage means for manually opening the throttle'valves' in sequence so that the primary throttle valve opens first; and vacuum-opera'tedmeans for holding the secondary throttle valve closed 'during initial opening movement of the primary valve with a force dependingon the vacuum therein and responsive to opening of the primary throttle valve to reduce the vacuum thereby to re- 'duce said force.

2. Amulti-stage fuel mixture supply system'for an internal combustion 'engine, said engine having an intake manifold, saidsystem comprising means providing a primary mixture conduit and a secondary mixture conduit adapted to supply a mixture of fuel and air to themanifold, 'aprimary throttle valve in the primary mixture conduit, a secondary throttle valve in the secondary'mixture conduit, lost-motion linkage means for manually opening the throttle valves in sequence so that the primary throttle valveopens first, and vacuum-operated means'for holding the secondary throttle valveclosed during initial opening movement of the primary valve with a force depending on the vacuum therein, said vacuum-operated means being connected to a source of vacuum wherein the vacuum decreases on opening the primary throttle valve, whereby said force is reduced on opening the primary throttle valve.

3. A multi-stage fuel mixture supply system as set forth in claim 2 wherein said vacuum-operated means is connected to the intake manifold.

4. A multi-stage fuel mixture supply system as set forth in claim 3 wherein said vacuum-operated means is connected to the intake manifold by means of a connection to the secondary mixture conduit posterior to the secondary' throttle valve.

5. A 'multi-stage fuel mixture supply system for an internal combustion engine comprising means providing a primary mixture conduit and a secondary mixture conduit adapted to supply a mixture of fuel and air to the engine, a primary throttle valve in the primary mixture conduit, a secondary throttle valve in the secondary mixture conduit, lost-motion linkage means for manually opening'the throttle valves in sequence so that the primary throttle valve opens first, vacuum-operated means for holding the secondary throttle valve closed during initial opening movement of the primary valve with a force depending on the vacuum therein, said vacuumope'rated means being connectedto a source of vacuum by'means including a control valve, and means responsive to opening of the primary throttle valve for actuating said control valve to reduce the vacuum in said vacuum-operated means.

6. A multi-stage fuel mixture system as set forth in claim 5 wherein said means for actuating said control valve acts prior to opening of the secondary throttle valve by said manual means.

7. A multi-stage fuel mixture supply system as set forth in claim 6 wherein said control valve is adapted upon actuation thereof to vent said vacuum-operated means.

8. A multi-stage fuel mixture supply system foran internal combustion engine comprising a primary carburetor and at least one secondary carburetor each'having a throttle valve, means for manually operating the throttle valve of the primary carburetor, means biasing the throttlevalve of the primary carburetor toward closed position, lost-motion linkage -means for opening the throttle'valve of the secondary carburetorin response to opening of the throttle valve of the primary carburetor beyond a'pre'determine'd intermediate position, and vacuum-operated means for holding the throttle valve of the secondary carburetor closed with a force depending on the vacuum therein and responsive to opening of the throttle valve of the primary carburetor to reducethe vacuumthereby toreduce saidforce as the throttle valve of theprirnary carburetor is opened from its closed to its said' predetermined intermediate position.

'9. *A multi-stage fuel mixture supply systemfor' an internal combustion 'engine,'said engine having an intake manifold, said' system comprising a primary carburetor and at least one secondary carburetor each having a throttle valve, means for manually operating the throttle valve of the primary carburetor, means biasing the throttle valve of the primary carburetor toward closed position, lost-motion linkage means for opening the throttle valve of the secondary carburetor in response to opening of the throttle valve of the primary carburetor beyond a'predetermined intermediate position, and vacurim-operated means for holding the throttle valve of the secondary carburetor closed with a force depending on the vacuum therein, said vacuum-operated means being connected to a source of vacuum wherein the vacuum decreases on opening the throttle valve of the primary carburetor, whereby said force is reduced as the throttle valve of the primary carburetor is opened from its closed to its said predetermined intermediate position.

-l0. A multi-stage fuel mixture supply system as set forth in claim 9 wherein said vacuum-operated means is connected to the intake manifold.

"11. A multi-stage fuel mixture supply system as set forth in claim 10 wherein said vacuum-operated means is connected to the intake manifold by means of a connection to the secondary carburetor posterior to the throttle valve thereof.

12. A multi-stage fuel mixture supply system for an internal combustion engine comprising a primary carburetor and 'at least one secondary carburetor each having a throttle valve, means for manually operating the throttle valve of the primary carburetor, means biasing the throttle valve of the primary carburetor toward closed position, lost-motion linkage means for opening the throttle valve of the secondary carburetor in response to opening of the throttle valve of the primary carburetor beyond a predetermined intermediate position, vacuumoperated means for holding the throttle valve'of the secondary' carburetor closed with 'a force depending on the vacuum therein, said vacuum-operated means being connected to a source of vacuum by means including a control valve, and means responsive to opening of the throttle valve of the primary carburetor from its closed to its saidipredetermined intermediate position for actuating said control valve to reduce the vacuum in said vacuumoperated means.

:13. A multi-stage fuel mixture supply system as set forth in claim 12 wherein said means for actuating said control valve acts before the throttle valve of the primary carburetor reaches its said predetermined intermediate position.

14. A multi-stage fuel mixture supply system as set forth in claim 13 wherein said control valve is adapted upon actuation thereof to vent said vacuum-operated means.

15..A multi-stage fuel mixture supply system for an internal combustion engine, said engine having an intake manifold, said system .comprising three dual carburetors mounted substantially in line on the manifold, the intermediate carburetor constituting a primary carburetor and each of the other two constituting a secondary carburetor, each carburetor having a .dual throttle valve, means for manually operatingthe throttle valve of the primary carburetor, means biasing the throttle valve of the primary carburetor toward closed position, lost-motion linkage 'connections for opening the throttle valves of the secondary carburetors in'response to opening of the throttle'valve of the primary carburetor beyond a predetermined intermediate position, each secondary carburetor having a vacuum motor mounted thereon with a connection between said motor and the respective throttle valve for holding the latter closed with a forcedepending on the vacuum in the motor, and means whereby the vacuum "in each'motor is responsive t'o th'ejop'ening of the throttle valve'of' the primarycarbur'et'orto reduce the vacuum in each motor as the'throttle valve of the 'prim'ary carburetor is opened.

16. A multi-stage fuel supply system as set forth in claim 15, wherein each motor is connected to the intake manifold.

17. A multi-stage fuel supply system as set forth in claim 16 wherein each motor is connected to the intake manifold by means of a connection to the respective secondary carburetor posterior to the throttle valve thereof.

18. A multi-stage fuel mixture supply system for an internal combustion engine, said engine having an intake manifold, said system comprising three dual carburetors mounted substantially in line on the manifold, the intermediate carburetor constituting a primary carburetor and each of the other two constituting a secondary carburetor, each carburetor having a dual throttle valve, means for manually operating the throttle valve of the primary carburetor, means biasing the throttle valve of the primary carburetor toward closed position, lost-motion linkage connections for opening the throttle valves of the secondary carburetors in response to opening of the throttle valve of the primary carburetor beyond a predetermined intermediate position, each secondary carburetor having a vacuum motor mounted thereon with a connection between said motor and the respective throttle valve for holding the latter closed with a force depending on the vacuum in the motor, said motors being connected to a source of vacuum by means including a control valve on the primary carburetor, and means connecting the throttle valve of the primary carburetor and said control valve for actuating said control valve when the throttle valve of the primary carburetor is opened from its closed to its said predetermined intermediate position to reduce the vacuum in the motors.

19. A multi-stage fuel mixture supply system as set forth in claim 18 wherein said means for actuating said control valve acts before the throttle valve of the primary carburetor reaches its said predetermined intermediate position.

References Cited in the file of this patent UNITED STATES PATENTS 

